The invention relates to an arrangement for inspecting a reactor vessel immersed in a water-filled tank, the arrangement comprising a driven mast-carriage which is arranged for movement around the upper opening of the reactor vessel and which has fixedly connected thereto a mast having extending therealong first track means for an inspection carriage arranged to carry inspection apparatus and provided with drive means for driving said inspection carriage along said track means.
When changing the inspection apparatus, which may comprise, for example, cameras, ultrasonic devices and like devices, it is necessary to lift the mast and mastcarriage from the tank and place them on the floor of the reactor hall. This is both troublesome and time consuming.